As an example of the speed changing transmission apparatus of the above-noted type, there was developed one disclosed in Patent Document 1. In the following, the construction disclosed in Patent Document 1 will be described. However, the purpose of this description is to explain the present application through comparison between the construction disclosed in this published gazette and the construction of the present application, the description should not be taken necessarily as admission of the construction disclosed in Patent Document 1 as prior art.
FIG. 17 is a diagram of a transmission apparatus of a tractor including a speed changing transmission apparatus S previously developed. As shown in this figure, this previously developed speed changing transmission apparatus S includes a stepless speed changing device 20A acting as a stepless speed changing section, and includes also a planetary transmission section P1, a clutch section C1, a third planetary transmission mechanism U3, and a brake B for acting on the third planetary transmission mechanism U. Numeral 10 shown in FIG. 17 represents a forward/reverse switchover device, numeral 3 denotes a rear wheel differential mechanism, and numeral 7 denotes a front wheel differential mechanism.
The stepless speed changing device 20A includes a variable displacement type hydraulic pump 23 having its pump shaft operably coupled via a main clutch 2 with an output shaft 1a of an engine 1, and a hydraulic motor 24 driven by pressure oil from this hydraulic pump 23.
The planetary transmission section P1 includes a first planetary transmission mechanism U1 and a second planetary transmission mechanism U2. Planet gears of the first planetary transmission mechanism U1 and planet gears of the second planetary transmission mechanism U2 are operably coupled with each other through meshing of coupling gear portions provided in the respective planet gears. The planet gears of the first planetary transmission mechanism U1 and planet gears of the second planetary transmission mechanism U2 are supported to a carrier 44 commonly used by the first planetary transmission mechanism U1 and the second planetary transmission mechanism U2.
The clutch section C1 includes a first clutch C11, a second clutch C12, a third clutch C13 and a fourth clutch C14. An input side rotational member (a) of the first clutch C11 is operably coupled via an operable coupling mechanism K1 to a ring gear of the second planetary transmission mechanism U2. An input side rotational member (b) of the second clutch C12 is operably coupled via a rotational shaft (c) to a sun gear of the second planetary transmission mechanism U2. An input side rotational member (d) of the third clutch C13 is operably coupled via an operable coupling mechanism K2 to the carrier 44 of the planetary transmission section P1.
The operable coupling mechanism K1, which operably couples the input side rotational member (a) of the first clutch C11 with the ring gear of the second planetary transmission mechanism U2, includes a clutch side transmission gear G1 meshed with the input side rotational member (a) of the first clutch C11, a planetary side transmission gear G2 meshed with the ring gear of the second planetary transmission mechanism U2, and a rotational shaft S1 coupled to the clutch side transmission gear G1 and the planetary side transmission gear G2. The operable coupling mechanism K2, which operably couples the input side rotational member (d) of the third clutch C13 with the carrier 44 of the planetary transmission section P, includes a clutch side transmission gear G3 meshed with the input side rotational member (d) of the third clutch C13, a planetary side transmission gear G4 meshed with the carrier 44, and a rotational shaft S2 coupled to the clutch side transmission gear G3 and the planetary side transmission gear G4.
The sun gear of the third planetary transmission mechanism U3 is operably coupled to an output side rotational member (e) of the first clutch C11 and the second clutch C12 and to an input side rotational member (f) of the third clutch C13. The carrier of the third planetary transmission mechanism U3 is operably coupled to an output side rotational member (g) of the third clutch C13 and the fourth clutch C14. The brake B can be switched over into an engaged state for applying a braking action on the ring gear of the third planetary transmission mechanism U3 and a disengaged state for releasing the braking action on the ring gear.
FIG. 19 is an explanatory view for explaining relationship between operational conditions of the respective clutches C11, C12, C13, C14 and the brake B of the previously developed speed changing transmission apparatus S and speed ranges of this speed changing transmission apparatus S. The mark “ENGAGED” in FIG. 19 represents engaged states of the respective clutches C11, C12, C13, C14 and the brake B. The mark “-” in FIG. 19 represents disengaged states of the respective clutches C11, C12, C13, C14 and the brake B.
FIG. 18 is an explanatory view for explaining relationship among speed changing conditions of the stepless speed changing device 20A of the previously developed speed changing transmission apparatus S, the speed ranges of the speed changing transmission apparatus S, and output speeds provided by a carrier shaft US (corresponding to “an output rotational body”) of the third planetary transmission mechanism U3. The vertical axis in FIG. 18 represents the output speed of the carrier shaft US. The horizontal axis in FIG. 18 represents speed changing conditions of the stepless speed changing device 20A. The sign “−MAX” in FIG. 18 denotes the speed changing condition of the maximum speed under reverse rotation transmitting condition of the stepless speed changing device 20A. The sign “0” on the horizontal axis represents the neutral condition of the stepless speed changing device 20A. The sign “+MAX” on the horizontal axis represents the speed changing condition of the maximum speed under forward rotation transmitting condition of the stepless speed changing device 20A.
As shown in these figures, with the previously developed speed changing transmission apparatus S, the output from the stepless speed changing device 20A and the drive force of the pump shaft of the stepless speed changing device 20A (the engine drive force not subjected to any speed changing action by the stepless speed changing device) are synthesized by the planetary transmission section P1. As the stepless speed changing device 20A is operated for speed change and as the first through fourth clutches C11, C12, C13, C14 and the brake B are switched over appropriately in association with the this speed changing operation, the synthesized drive force outputted from the planetary transmission section P1 is provided in any one of the first through fourth speed stages and in each speed stage, the force is steplessly speed-changed to be outputted from the carrier shaft US of the third planetary transmission mechanism U3.
Patent Document 1: Japanese Patent Application “Kokai” No. 2007-092949 (JP2007-092949 A).